1. Field of the Invention
The present invention relates generally to fluidized catalytic cracking. More particularly, the present invention relates to apparatus and processes for improved separation of converted hydrocarbon oil fractions from catalyst within a fluidized catalytic cracking system.
2. Summary of the Prior Art
Hydrocarbon feedstocks such as petroleum oil fractions may be advantageously converted to lower boiling, more valuable hydrocarbon products such as gasoline by means of fluidized ctalytic cracking reactions. see, for example, U.S. Pat. Nos. 3,243,265, 3,123,547; and 3,841,843. The disclosure of copending application Ser. No. 238,380 filed Feb. 26, 1981, assigned to the assignee of the present application, is incorporated herein by this reference thereto.
In a known catalytic cracker unit an input feed of a mixture of hydrocarbon oil and catalyst is reacted in a riser conduit. The riser is associated with a reactor vessel, either running through the vessel or external to the vessel. In the latter case, the top of the riser generally includes a U-turn to first enter a side wall of the reactor vessel and then discharge downwardly into the reactor vessel. Spent catalyst from this reaction is allowed to fall through the vessel which contains a stripping section. Steam is generally introduced into the lower end of the vessel to aid in displacing hydrocarbons from the catalyst. Gaseous oil conversion products are conveyed upwardly and are separated from entrained catalyst in cyclone separators arranged at the upper portion of the vessel. Spent catalyst is removed from a lower portion of the vessel and is conveyed to a regenerator.
It has been found that the known designs tend to discharge large quantities of catalyst, particularly in the form of fines, with the oil conversion products conveyed to the upper portion of the reactor vessel. Further, the baffle arrangements of some of the prior art units have tended to cause slumped areas of catalyst within the reactor vessel. The slumped catalyst areas may raise the temperature of the unit and interfere with proper catalyst circulation thereby lowering the efficiency of the unit. Also, catalyst/steam contact is inhibited within the slumped catalyst areas so that a lesser amount of oil conversion products is removed from the catalyst.
Therefore, the search has continued for improved fluidized catalytic cracking apparatus and processes which are more effective in producing converted hydrocarbon oil products while avoiding the problems of the prior art.